Review Question - QID 3047

With the wrist extended force transmission is shifted to a greater extent through the scaphoid and the scaphoid fossa.

The position of the wrist can change the pattern of force transmission across the joint. With the wrist in neutral force is transferred across the joint via the lunate fossa and scaphoid fossa almost equally (slight predominance to the scaphoid fossa). However, with the wrist extended force transmission is shifted to pass even more via the scaphoid fossa, and less via the lunate fossa. This is a proposed explanation for scaphoid fractures resulting from falls onto an outstretched hand with the wrist extended.

Majima et al. tested force transmission through the wrist in different positions in a 3 dimensional rigid body spring model from CT images. They found that force through the scaphoid fossa increased from 52% to 62% with extension of the wrist (p<0.05). Similarly, in the midcarpal joint force transmitted across the scaphoid increased from 60% to 69% (p<0.05).

Weber et al. performed a cadaveric study of wrist injury. They found that with the wrist extended, the force applied to the palm was increased 4 times as it transmitted across the scaphoid. They describe the waist of the scaphoid as a location of concentrated force and theorize this is why waist fractures are common in injuries with wrist extended.

Incorrect answers:
Answers 1, 2, 3, 5: These do not appropriately describe force transmission based on wrist position.